In this scientific publication, a new sensor approach for status monitoring, such as state of charge and state of health, of lithium ion batteries by using special Bragg gratings inscribed into standard optical glass fibers is presented. In addition to well-known core gratings, embedded into the anode of 5 Ah lithium ion pouch cells as a strain monitoring unit, the manufacturing of a surface cladding waveguide Bragg grating sensor incorporated into the cell’s separator, that is sensitive to changes of the refractive index of the surrounding medium, is demonstrated. On the basis of the experiments carried out, characteristics of the cell behavior during standard cyclization and recognizable marks in subsequent post-mortem analyses of the cell components are shown. No negative influence on the cell performance due to the integrated sensors have been observed; however, the results show a clear correlation between fading cell capacity and changes of the interior optical signals. Additionally, with the novel photonic sensor, variations in the electrolyte characteristics are determinable as the refractive index of the solution changes at different molar compositions. Furthermore, with the manufactured battery cells, abuse tests by overcharging were conducted, and it was thereby demonstrated how internal battery sensors can derive additional information beyond conventional battery management systems to feasibly prevent catastrophic cell failures. The result of the research work is an early stage photonic sensor that combines chemical, mechanical and thermal information from inside the cell for an enhanced battery status analysis.

Mechanical and electrochemical stability are key issues for large-scale production of solid state Li-ion batteries. Polymer electrolytes can provide good ionic conductivity, but mechanical strength needs to be improved. In this study, we investigate the correlation of mechanical and electrical properties of poly (ethylene oxide) (PEO)-based solid electrolytes for Li-ion batteries. The influence of alumina and LiClO₄ addition are investigated. Differential scanning calorimetry (DSC) is used to study the thermal behavior of salt-free and salt-containing samples and to identify the melting temperature. Dynamic mechanical analysis reveals the elastic properties as a function of temperature. Electrochemical properties are investigated using impedance spectroscopy. It is found that addition of alumina increases mechanical strength, while LiClO₄ decreases it. Addition of LiClO₄ and Al₂O₃ increases ionic conductivity and improves mechanical properties. However, there is no overlapping window of high mechanical strength and high ionic conductivity.

New energy systems such as all-solid-state battery (ASSB) technology are becoming increasingly important today. Recently, researchers have been investigating the transition from the lab-scale production of ASSB components to a larger scale. Poly(ethylene oxide) (PEO) is a promising candidate for the large-scale production of polymer-based solid electrolytes (SPEs) because it offers many processing options. Hence, in this work, the thermal processing route for a PEO-Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) SPE in the ratio of 20:1 (EO:Li) is investigated using kneading experiments. Here, we clearly show the sensitivity of PEO during thermal processing, especially for high-molecular-weight PEO (M_w = 600,000 g mol⁻¹). LiTFSI acts as a plasticizer for low-molecular-weight PEO (M_w = 100,000 g mol⁻¹), while it amplifies the degradation of high-molecular-weight PEO. Further, LiTFSI affects the thermal properties of PEO and its crystallinity. This leads to a higher chain mobility in the polymer matrix, which improves the flowability. In addition, the spherulite size of the produced PEO electrolytes differs from the molecular weight. This work demonstrates that low-molecular-weight PEO is more suitable for thermal processing as a solid electrolyte due to the process stability. High-molecular-weight PEO, especially, is strongly influenced by the process settings and LiTFSI.

Rylene imides (RIs) are attractive organic battery materials because of the inherent modularity of the molecules. While strong aggregation of RIs is disadvantageous for fast lithium‐ion transport in the organic active material, decreasing the solubility of the RIs in battery electrolytes is essential to avoid performance fading. Therefore, the design and synthesis of RIs for lithium batteries is a non‐trivial task that must, among other considerations, balance lithium‐ion transport in the solid material vs. low solubility by controlling aggregation and packing. We have chosen triphenylamine (TPA) as a substituent which disrupts the aggregation but maintains a low solubility due to increased aromaticity of TPA. We have synthesized three RIs with one, two, and four aromatic units in the core. All of them showed stable specific capacity over 300 charge‐discharge cycles. The batteries also showed specific capacities close to their theoretical capacities with 97–99 % coulombic efficiency. The maximum specific energy and specific power were 197 mWh g⁻¹ and 37 mW g⁻¹, respectively.

All-solid-state battery (ASSB) technology is a new energy system that reduces the safety concerns and improves the battery performance of conventional lithium-ion batteries (LIB). The increasing demand for such new energy systems makes the transition from laboratory scale production of ASSB components to larger scale essential. Therefore, this study investigates the dry extrusion of poly(ethylene oxide):lithium bis (trifluoromethylsulfonyl)imide (PEO:LiTFSI) all-solid-state electrolytes at a ratio of 20:1 (EO:Li). We investigated the influence of different extruder setups on the product quality. For this purpose, different screw designs consisting of conveying, kneading and mixing elements are evaluated. To do so, a completely dry and solvent-free production of PEO:LiTFSI electrolytes using a co-rotating, intermeshing, twin-screw extruder under an inert condition was successfully carried out. The experiments showed that the screw design consisting of kneading elements gives the best results in terms of process stability and homogeneous mixing of the electrolyte components. Electrochemical impedance spectroscopy was used to determine the lithium-ion conductivity. All electrolytes produced had an ionic conductivity (σ_ionic) of (1.1–1.8) × 10⁻⁴ S cm⁻¹ at 80 °C.